Dogs and inanimate objects are used as mother substitutes in an investigation of the effects of maternal attributes on psychosocial development. Monkeys live continuously in outdoor kennels with their substitute mothers and are regularly placed in complex environments designed to encourage a broad range of instrumental activities. One group of monkeys is raised with dogs that are free to roam in the exposure environments. A second group of monkeys is also raised with dogs, but the dog is restricted to one region within each of the complex environments. The third group of monkeys is raised with inanimate surrogates, also restricted to one location in each complex environment. Assessment procedures focus on the attachment process (strength, specificity, perceptual aspects) and on problem-solving ability, using social and nonsocial cues. Results to date indicate major differences in aspects of attachment between the monkeys raised with inanimate surrogates and the two dog-raised groups, whereas the primary contrasts in problem-solving performance are between the Free Dog and the two restricted groups.